I bought a pair of new shock absorbers for my car today. When i went to the workshop and open up i did a compression on the pistons. i found that one of the shock piston return faster than the other. Both are of the same brand and specs. What could be the cause of it?

Could be an effect of how they were stored - some shocks control both bump (compression) and rebound (extension)...
– Solar MikeMay 31 at 13:56

i suspect that also. when i open up both shocks from the boxes it looks like one of it has been dealt with. both of these shocks has different numbering. it could be one of it is an old batch and stroed for a long time. Does this mean it is bad as one of them takes a longer time to return whereas the other one just shoots out in less than 10 secs.
– Dave CytMay 31 at 14:12

2 Answers
2

It would be helpful to know what car these are for and what location they are fitted in.

Remember that on most applications, the return of the suspension to it's "normal" position is done by the spring, not the damper. All that the dampers are there for is to absorb the compression from bumps.

What you'd be better doing is looking at how they respond to compression as this is where they're doing their "work".

it is for toyota previa 2003 model (acr30). The rear shocks are from japan under the brand KYB. From my findings i suspect one of the shocks might be of an old batch due to a different batch number and that it has been stored for a long time.Does this mean it is bad as one of them takes a longer time to return whereas the other one just shoots out in less than 10 secs.
– Dave CytMay 31 at 14:13

Return rate on new shocks out of the box is irrelevant. It's how they perform once installed that matters. Two shocks can have two different rates right out of the box and work perfectly fine in the vehicle. It all depends on how they were stored.

what do you mean how they were stored? Does it affect the performance of the shocks in storage?
– Dave CytJun 2 at 13:30

Modern shocks/struts contain oil and nitrogen gas. If they're stored upright, the gas sits above the oil. If horizontal and shaken in transit, the nitrogen can mix with the oil forming bubbles. If you depress the shock with bubbles, it will have a different return rate than a shock that doesn't have bubbles. Once installed, the nitrogen separates and the shock operates normally. So return rate out of the box has nothing to do with how they'll perform once installed.
– user9181Jun 3 at 18:51